Interventional Radiology · Peripheral vascular interventions · 1.0

Rutherford classification: acute and chronic limb ischaemia categories

The Rutherford SVS/ISCVS reporting standards classify acute limb ischaemia into categories I, IIa, IIb and III by sensory loss, motor deficit and Doppler signals, and chronic lower-limb ischaemia into grades 0-III with categories 0-6 from asymptomatic disease to major tissue loss.

Purpose

To provide standardised severity criteria for reporting lower extremity ischaemia. Two separate scales are used because acute and chronic ischaemia must not be mixed: an acute scale (I, IIa, IIb, III) based on viability that drives the urgency and type of revascularisation, and a chronic scale (grades 0-III, categories 0-6) based on symptoms plus objective haemodynamic criteria. Category IIa was created specifically to identify limbs in which there is still time for a catheter-directed thrombolytic approach.

Scale	Category	Description / prognosis	Sensory loss	Muscle weakness	Doppler signals (arterial / venous)
Acute	I - Viable	Not immediately threatened	None	None	Audible / audible
Acute	IIa - Marginally threatened	Salvageable if promptly treated	Minimal (toes) or none	None	Inaudible / audible
Acute	IIb - Immediately threatened	Salvageable with immediate revascularisation	More than toes, associated with rest pain	Mild to moderate	Inaudible / audible
Acute	III - Irreversible	Major tissue loss or permanent nerve damage inevitable	Profound, anaesthetic	Profound, paralysis (rigor)	Inaudible / inaudible
Chronic (grade 0)	0	Asymptomatic - no haemodynamically significant occlusive disease	Not applicable	Not applicable	Normal treadmill or reactive hyperaemia test
Chronic (grade I)	1	Mild claudication	Not applicable	Not applicable	Completes treadmill exercise; ankle pressure after exercise above 50 mmHg but at least 20 mmHg below the resting value
Chronic (grade I)	2	Moderate claudication	Not applicable	Not applicable	Between categories 1 and 3
Chronic (grade I)	3	Severe claudication	Not applicable	Not applicable	Cannot complete standard treadmill exercise and ankle pressure after exercise below 50 mmHg
Chronic (grade II)	4	Ischaemic rest pain	Not applicable	Not applicable	Resting ankle pressure below 40 mmHg, flat or barely pulsatile ankle or metatarsal PVR, toe pressure below 30 mmHg
Chronic (grade III)	5	Minor tissue loss - non-healing ulcer, focal gangrene with diffuse pedal ischaemia	Not applicable	Not applicable	Resting ankle pressure below 60 mmHg, ankle or metatarsal PVR flat or barely pulsatile, toe pressure below 40 mmHg
Chronic (grade III)	6	Major tissue loss extending above transmetatarsal level; functional foot no longer salvageable	Not applicable	Not applicable	Same objective criteria as category 5

How to use it

The acute scale is bedside-driven: sensory loss, muscle weakness and pedal Doppler signals. Neither IIa nor IIb has audible pedal arterial signals; the discriminator is neurological. Any motor loss, or sensory loss extending above the toes with persistent rest pain, defines IIb.
Category IIa exists because of thrombolysis. The 1997 revision subdivided category II explicitly to identify limbs in which there is time for angiography and catheter-directed lysis under close surveillance, whereas IIb requires immediate revascularisation - favouring embolectomy, mechanical or aspiration thrombectomy over lysis alone.
Category III has absent venous as well as arterial Doppler signals, with profound anaesthesia and paralysis with rigor or skin marbling. Major amputation or permanent neuromuscular damage is predicted regardless of therapy, and reperfusion carries the risk of rhabdomyolysis and hyperkalaemia.
In the chronic scale, grades II and III (categories 4, 5 and 6) constitute chronic critical ischaemia, now termed chronic limb-threatening ischaemia in the 2019 Global Vascular Guidelines. Higher ankle and toe pressure thresholds are used for tissue loss than for rest pain because healing an ulcer needs more perfusion pressure than preserving intact tissue.
Rutherford grades severity only. Anatomical disease burden is described separately (GLASS in the GVG), and limb threat incorporating wound and infection is staged by WIfI. Absolute pressures rather than the ABI were chosen because a given ABI can represent a wide range of true perfusion pressures.

Common mistake

Mixing the two scales - quoting 'Rutherford III' for a patient with rest pain, when acute category III means an irreversibly ischaemic limb for primary amputation while rest pain is chronic category 4. The second error is offering slow catheter-directed thrombolysis to a category IIb limb with established motor deficit, and the third is relying on an ankle pressure of 30 mmHg to separate acute categories I and II, a misinterpretation the 1997 revision specifically criticised in favour of audible pedal arterial signals.

Exam pearl

Acute: sensory loss confined to toes with no weakness = IIa (time for lysis); sensory loss beyond the toes with rest pain plus any motor loss = IIb (immediate revascularisation); absent venous Doppler with paralysis and rigor = III (amputate). Chronic: 4 = rest pain, 5 = minor tissue loss, 6 = major tissue loss; 4-6 = chronic limb-threatening ischaemia.

Viva questions

What separates Rutherford acute category IIa from IIb?: Both are salvageable and neither has audible pedal arterial Doppler signals. IIa has minimal sensory loss limited to the toes or none, with no muscle weakness. IIb has sensory loss extending beyond the toes with persistent ischaemic rest pain, and mild to moderate muscle weakness. Any motor loss puts the limb into IIb.
Why was category II subdivided in the 1997 revision?: Because of catheter-directed thrombolysis. The original three-category scheme could not identify the subgroup with absent pedal signals but only mild or evanescent sensory loss in whom limb salvage was achievable with a more time-consuming lytic approach. IIa allows time for angiography and lysis under close surveillance; IIb requires immediate revascularisation.
How does the acute category change your interventional strategy?: Category I allows deliberate evaluation and even non-operative management with anticoagulation, with elective revascularisation. Category IIa permits catheter-directed thrombolysis or endovascular thrombectomy but promptly. Category IIb needs immediate flow restoration, so surgical embolectomy, mechanical or aspiration thrombectomy, or a hybrid approach with adjunctive lysis is preferred. Category III is not revascularised for salvage.
What findings define Rutherford acute category III?: Profound anaesthetic sensory loss and paralysis with muscle rigor, absent distal capillary skin flow, sometimes skin marbling, and inaudible arterial and venous Doppler signals over the pedal vessels. Major amputation or permanent neuromuscular damage is inevitable regardless of therapy, and reperfusion risks rhabdomyolysis and hyperkalaemia.
Why does the acute scale contain no time criterion?: The 1997 standards deliberately excluded temporal criteria such as 6 to 12 hours because the extent of tissue damage also depends on the site of occlusion, existing collateral circulation and other factors, so a fixed duration does not reliably predict viability.
Which chronic Rutherford categories constitute chronic limb-threatening ischaemia?: Grades II and III, that is categories 4, 5 and 6 - ischaemic rest pain, minor tissue loss with non-healing ulcer or focal gangrene and diffuse pedal ischaemia, and major tissue loss above the transmetatarsal level. Categories 1 to 3 are claudication. The term was chronic critical ischaemia in 1997 and is now chronic limb-threatening ischaemia.
Why are the pressure thresholds higher for tissue loss than for rest pain?: Rest pain uses an ankle pressure below 40 mmHg and toe pressure below 30 mmHg, whereas tissue loss uses an ankle pressure below 60 mmHg and toe pressure below 40 mmHg. Healing an ulcer or a distal amputation, particularly with secondary infection, requires more perfusion pressure than merely preserving intact tissue.
Why did Rutherford use absolute ankle pressures rather than the ABI to define advanced chronic ischaemia?: Because actual perfusion pressure is what matters. A single ABI value can correspond to a wide range of ankle pressures depending on systemic blood pressure, so two patients with the same ABI may differ substantially in whether they have ischaemic pain. Pressure indices such as the ABI remain better for comparing groups and following an individual over time.
How does Rutherford relate to WIfI, TASC II and GLASS?: Rutherford grades clinical severity only. WIfI stages limb threat by wound, ischaemia and foot infection; TASC II and GLASS describe anatomical lesion complexity to guide revascularisation strategy. They are complementary and should not be used interchangeably.